1. Field of the Invention
The present invention relates to an inorganic composition capable of being sintered at a low temperature and having a low dielectric constant and more specifically to an inorganic composition which is mainly used for preparing a multilayer ceramic printed wiring board for mounting a very fast VLSI element, capable of being sintered at a low temperature of the order of not more than 1,000.degree. C. and has a low dielectric constant and high strength.
2. Description of the Prior Art
Until now, semiconductor elements such as IC's and LSI's have been mounted on a printed wiring board of, for instance, a glass-epoxy or an alumina ceramic substrate, but there have been increasingly required for the development of a substrate for mounting these elements which carries a fine pattern of distributing wire in a high density and which is capable of rapid transmission of signals, capable of being operated at a high frequency and capable of rapid radiation of heat as semiconductor elements have been improved in that the degree of integration thereof is increased, that they are more and more miniaturized and that they can operate at a higher speed. However, the conventional printed wiring boards suffer from various problems of insufficient plating ability of through holes, insufficient working characteristics, low adhension during lamination and high heat deformation at a high temperature, and the conventional printed boards are correspondingly limited in the density of distributing wire patterns to be printed. For this reason, any printed wiring board carrying a fine distributing wire pattern of a desired density has not yet been put into practical use and, therefore, ceramic substrates have attracted much attention recently.
However, the alumina substrates must be sintered at a high temperature of not less than 1500.degree. C. and accordingly, the conductive materials usable for printing distributing wire patterns which are co-fired are limited to a refractory or high-melting metal having relatively high resistivity such as W, Mo or the like. Thus, the degree of fineness of the wiring pattern is limited while taking into consideration the transmission loss of pulse signals.
Under such circumstances, there have been proposed low temperature sintering multilayer ceramic substrates. Examples of insulating ceramic materials in such substrates include those comprising composites of alumina and glass and those comprising crystallized glass. For instance, Japanese Unexamined Patent Publication (hereinafter referred to as "J. P. KOKAI") No. Hei 3-252353 (which corresponds to a pending U.S. Ser. No. 07/661,606 filed on Feb. 28, 1991) discloses a ternary system comprising alumina, quartz glass and borosilicate glass; and J. P. KOKAI Nos. Hei 3-252354 and Hei 3-141153 disclose ternary systems comprising quartz (.alpha.-quartz), quartz glass and borosilicate glass or lead borosilicate glass. All of these ceramic materials are sintered at a temperature of not more than 1,000 .degree. C. and accordingly, a low-melting metal having low resistivity such as Au, Ag-Pd, Cu or the like can be used as a conductive material for printing distributing wire patterns. Moreover, it is also possible to use the green sheet lamination technology which is very effective for obtaining substrates carrying fine distributing wire patterns of high densities.
On the other hand, it is inevitable that the dielectric constants of materials for substrates must be reduced to a level as low as possible to speed up the transmission of signals since the transmission delay time of pulse signals is proportional to the root of the dielectric constant of a particular substrate material selected. For instance, the dielectric constant of alumina is about 10 and those of low temperature sintering ceramic substrates are lower than that of alumina. However, the reduction of dielectric constants of substrate materials is still insufficient for achieving high transmission velocity of signals. There has thus been investigated the use of those having low dielectric constants which comprise, as host ceramics, quartz glass and other materials having low dielectric constants such as cordierite and mullite in place of alumina and the use of glass components having low dielectric constants such as those mainly comprising silicon oxide or boron oxide. These materials have sufficiently low dielectric constants, but suffer from problems of lowering of mechanical properties such as strength. This problem becomes more conspicuous in producing substrates and in mounting semiconductor elements.